A stabilizer bushing is an example of an anti-vibration rubber member. The stabilizer bushing is fixed to a vehicle body through a bracket. A stabilizer bar is disposed in a holding hole of the stabilizer bushing.
For example, during turning of the vehicle, a centrifugal force causes the outer wheel side of the suspension to sink downward while the inner wheel side elongates. This twists the stabilizer bar. Utilizing an elastic restoring force against such torsion, the stabilizer bar works to lift up the outer wheel side of the suspension. Thus, the stabilizer bar maintains the vehicle horizontal.
When the stabilizer bar is twisted or when the twisted stabilizer bar recovers due to the elastic restoring force, the stabilizer bar outer circumferential surface and the stabilizer bushing inner circumferential surface slide relative to one another. Higher friction resistance during such sliding may cause more abnormal noise (what is called a stick slip noise). Higher friction resistance during such sliding may also reduce the riding comfort of the vehicle.
In view of these points, a liner made of polytetrafluoroethylene (PTFE) with a small friction coefficient is conventionally inserted into a holding hole. The inner circumferential surface of the liner is then brought in sliding contact with the outer circumferential surface of the stabilizer bar. However, the PTFE liner is relatively expensive. Therefore, if the PTFE liner is used, the cost of producing the stabilizer bushing increases.
Hence, stabilizer bushings that do not require a PTFE liner have been developed. For example, Patent Documents 1 and 2 describe a stabilizer bushing that has a rubber elastic body made of a self-lubricating rubber, a coating film, and a lubricating film. A holding hole is formed on the radially inner side of the rubber elastic body. A stabilizer bar is disposed in the holding hole. The coating film covers the inner circumferential surface of the holding hole. A bleeding lubricant included in the self-lubricating rubber penetrates the coating film and oozes onto the surface of the coating film to form the lubricating film. The lubricating film is in sliding contact with the stabilizer bar. In the case where the lubricating film is insufficient on a portion, the coating film containing the bleeding lubricant is exposed from this portion and comes into sliding contact with the stabilizer bar. According to the stabilizer bushing described in Patent Documents 1 and 2, primarily the lubricating film and supplementarily the coating film are in sliding contact with the stabilizer bar. Consequently, the friction resistance between the stabilizer bushing and the stabilizer bar is reduced.